The long-term goals of this project are to understand the role of the cyclic GMP (cGMP)-dependent protein kinase (cG-kinase) in the normal uterus and how cGMP signaling through this enzyme is modified by progesterone. Cyclic GMP is a second messenger best known for its role as a vasorelaxant. This cyclic nucleotide mediates many effects of nitric oxide and atrial natriuretic peptides by activating the cG-kinase. Preliminary data support the hypothesis that progesterone-dominated physiological states (i.e., pregnancy) result in a down regulation of immunoreactive uterine cG-kinase. The major area of focus in this proposal is to define the mechanism of down regulation of cG-kinase expression by progesterone in human uterine smooth muscle. These studies rely on human uterine smooth muscle cells (SMC) for defining cellular and molecular mechanisms of progesterone action. Three specific aims are proposed. AIM 1: To characterize the progesterone regulation of uterine cG-kinase. The hypothesis that will be tested is that progesterone decreases expression of cG-kinase in a time- and concentration-dependent manner. AIM 2: To determine the specificity of progesterone regulation of uterine cG-kinase. The hypothesis that will be tested is that progesterone down regulates cG- kinase via binding to a specific progesterone receptor. Analogs of progesterone and glucocorticoids including medroxyprogesterone acetate, R5020, ORG2058, norethynodrel, 17alpha-hydroxyprogesterone and a cell impermeant progesterone will be used to study specificity of progesterone effects. Selective and nonselective antagonists of both progesterone and glucocorticoid receptors including RU486, RU5O.331, ZK112.993, ZK98.299, and RU43.044 will be used to determine which receptor mediates the effects of progesterone. AIM 3: To define the mechanism of regulation of cG-kinase in uterine SMC. The hypothesis that will be tested is that progesterone down regulates cG-kinase expression by altering synthesis of new protein or mRNA or the stability of existing protein or mRNA. Clarification of the regulation of cG-kinase by progesterone will provide insight into the design of tocolytic therapies based on nitric oxide and cGMP actions.